1. Field of the Invention
The present invention relates to an ultrasonic motor using, for example, a transducer such as a piezoelectric element.
2. Description of the Related Art
Recently, attention has been paid to an ultrasonic motor using the vibration of a transducer such as a piezoelectric element as a new motor replacing an electromagnetic type motor. This ultrasonic motor is superior to a conventional electromagnetic type motor in being capable of obtaining low-speed high thrust without gears, having high holding force, having high resolution, being low noise, producing no magnetic noise, and the like.
More specifically, for example, in this motor, a transducer body formed from an ultrasonic transducer is pressed against a rotor as a driven member through a driving element to generate a frictional force between the driving element and the rotor, thereby driving the rotor with the frictional force.
More specifically, simultaneously generating longitudinal vibration and twisting vibration in the ultrasonic transducer will generate elliptic vibration by combining the vibrations in an end face of the ultrasonic transducer, thereby rotating the rotor by using the elliptic vibration. As a technique associated with this ultrasonic motor, for example, the following technique is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 9-85172.
That is, Jpn. Pat. Appln. KOKAI Publication No. 9-85172 discloses an ultrasonic motor including a rod-like elastic body, a plurality of holding elastic bodies provided on a side surface of the rod-like elastic body so as to be integrated with the rod-like elastic body, a plurality of multilayer piezoelectric elements each having two ends held by the plurality of holding elastic bodies, a plurality of vibration detection piezoelectric elements provided between the multilayer piezoelectric elements and the holding elastic bodies, a friction element provided on an end face of the rod-like elastic body, a rotor which is placed while being pressed against the friction element by a pressing means, and a power supply means for applying, to each of the plurality of pairs of multilayer piezoelectric elements, alternating voltages having a phase difference, which have a predetermined frequency and magnitude (amplitude) corresponding to the phase or amplitude of a signal output from the vibration detection piezoelectric elements.
This motor includes the plurality of pairs of multilayer piezoelectric elements. More specifically, the displacing direction of each of the multilayer piezoelectric elements and the longitudinal direction of the rod-like elastic body define a predetermined acute angle, and each pair of the multilayer piezoelectric elements tilt in opposite directions.
The ultrasonic motor disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-85172 excites elliptic vibration by simultaneously exciting longitudinal vibration and twisting vibration in the rod-like elastic body, thereby driving to rotate the rotor using the friction element.
More specifically, according to the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-85172, one pair or a plurality of pairs of multilayer piezoelectric elements are held between the rod-like elastic body having concave portions in which the multiplayer piezoelectric elements can be inserted and the holding elastic bodies. The holding elastic bodies are fixed to the rod-like elastic body with screws while they are abutted on the multilayer piezoelectric elements to apply compressive stress to them.
When, therefore, the structure disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-85172 is to be used, holding elastic bodies for fixing piezoelectric elements become essential constituent elements, and it is necessary to form concave portions in a rod-like elastic body to accommodate the holding elastic bodies and the piezoelectric elements. It is therefore difficult to simplify and reduce the size of the structure of a transducer body by using the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-85172.